1. Field of the Invention
The present invention relates to semiconductor devices and display devices using the semiconductor devices, and further manufacturing methods thereof.
2. Description of the Related Art
There are a wide variety of metal oxides and such metal oxides are used for various applications. Indium oxide is a well-known material and is used as a transparent electrode material needed for a liquid crystal display and the like.
Some metal oxides exhibit semiconductor characteristics. Examples of such metal oxides having semiconductor characteristics include tungsten oxide, tin oxide, indium oxide, and zinc oxide. A thin film transistor having such metal oxide having semiconductor characteristics in its channel formation region has been proposed (Patent Documents 1 to 4 and Non-Patent Document 1).
As metal oxides, multi-component oxides as well as single-component oxides are known. For example, homologous compound, InGaO3(ZnO)m, (m is natural number) is known as a multi-component oxide having In, Ga and Zn (Non-Patent Documents 2 to 4).
Furthermore, it is confirmed that an oxide semiconductor including such an In—Ga—Zn-based oxide is applicable to a channel layer of a thin film transistor (Patent Document 5 and Non-Patent Documents 5 and 6).
In a conventional technique, amorphous silicon or polycrystalline silicon has been used for a thin film transistor (a TFT) provided for each pixel of an active matrix liquid crystal display. However, in place of these silicon materials, attention has been attracted to a technique for manufacturing a thin film transistor including such a metal oxide semiconductor described above. For example, in Patent Documents 6 to 9, a technique in which a thin film transistor is formed using zinc oxide or an In—Ga—Zn—O-based oxide semiconductor as a metal oxide semiconductor film and is used as a switching element or the like of an image display device is described. It is also known that semiconductors including elements of Group 14 other than silicon and compound semiconductors other than the oxide semiconductor described above can be used for channel layers of transistors.
In addition, an oxide semiconductor film can be deposited at temperature of 300° C. or lower by a sputtering method or the like, and thin film transistors having channel formation regions formed using oxide semiconductor can be easily formed in a wide region of a large substrate. Thus, application of oxide semiconductors to active matrix display devices has been expected.